1. Field of the Invention
Exemplary embodiments of the present invention generally relate to a grid electrode provided to a scorotron charger, an image forming apparatus including the grid electrode provided to the scorotron charger, and a process cartridge integrally including the scorotron charger having the grid electrode.
2. Discussion of the Related Art
Related-art electrophotographic image forming apparatuses generally include a charging unit that uses a configuration employing a corotron charger or a scorotron charger to uniformly charge a surface of a photoconductive element or photoconductor. Such a known scorotron charger may be provided with a shield case to include components such as a charge wire and a grid electrode. The charge wire may be disposed facing or opposed to the surface of the photoconductor with a given gap therebetween. The grid electrode may be planar-shaped with aperture patterns, and be disposed closer to the photoconductor than the charge wire is.
High-voltage energization of the charge wire causes corona discharge, so that the surface of the photoconductor can be charged to a substantially same potential as the grid electrode.
To achieve a desired ability to control the potential of the photoconductor (hereinafter, “potential controllability”), it is preferable that the photoconductor and the grid electrode are equally spaced therebetween over an entire area in a lateral direction of the grid electrode or in a moving direction or rotation direction of the photoconductor.
When the photoconductor includes a flat belt, the above-described arrangement can be accomplished easily, even with respect to apertures such as a plurality of long mesh apertures, for example, hexagonally arranged apertures.
However, most photoconductors are drum-shaped, that is, with curvature, and therefore it is difficult to dispose the grid electrode along the curvature of the drum-shaped photoconductor when the grid electrode has apertures of hexagonal shape or stripe shape.
There has been an attempt to arrange a related-art grid electrode along the curvature of a drum-shaped photoconductor. However, when the related-art grid electrode that has patterns of a plurality of hexagons and stripes is pulled or extended from each end in a longitudinal direction thereof, tension cannot be evenly provided or uniformly distributed across the related-art grid electrode. Specifically, the tension may be less at the center portion of the grid electrode than at both end portions of the grid electrode. Therefore, the grid electrode cannot form a circular arc, and thus the distance between the photoconductor and the grid electrode cannot be kept constant, which means that the charging of the photoconductor surface is uneven and results in uneven density of the resulting reproduced image and hence poor image quality.
In another attempt, a different related-art grid electrode has been made flat and disposed facing the surface of a drum-shaped photoconductor. However, this configuration causes unevenness of distances between the flat-shaped grid electrode and the drum-shaped photoconductor. Specifically, a distance between the flat-shaped grid electrode and the drum-shaped photoconductor is shortest at a center portion in the lateral direction or across the grid electrode with respect to the photoconductor, and the distance becomes greater as the portion where the flat-shaped grid electrode faces the photoconductor moves away from the center portion toward the both ends in the lateral direction of the grid electrode. As a result, the potential controllability of the photoconductor deteriorates extremely at both ends thereof.
Yet another attempt has been made to arrange a related-art grid electrode along the curvature of a drum-shaped photoconductor. However, no data for the grid electrode including its patterns was disclosed and no examples of effective patterns to improve the potential controllability and charging nonuniformity were shown.
Yet another attempt has been performed using a grid electrode having apertures of linear patterns in a longitudinal direction only. The grid electrode was provided with a fitting member arranged at a center part of both ends in a lateral direction or across the apertures of linear patterns so as to extend the grid electrode in a longitudinal direction thereof by engaging each fitting member with a hook mounted on another component or unit in an image forming apparatus.
With the above-described configuration, the intervals or space between the linear-shaped apertures of the grid electrode and the drum-shaped photoconductor can be constantly provided in the lateral direction of the grid electrode. However, it is difficult to provide constant intervals or space between the grid electrode and the drum-shaped photoconductor over an entire area in the longitudinal direction of the grid electrode. Therefore, potential deviations in the longitudinal direction of the drum-shaped photoconductor were generated, which is likely to cause unevenness in the charge applied to the photoconductor, resulting in unevenness or non-uniformity in the density of reproduced images.